To test the hypothesis that blood to brain glucose transport is reduced in patients with poorly controlled IDDM and is increased following recent antece-dent hypoglycemia in patients with IDDM blood-to-brain glucose transport (as well as brain glucose metabolism is measured with [1-11C] glucose and position emission tomography, first, in patients with poorly controlled IDDM and matched nondiabetic controls and second, in healthy subjects on two occasions, once following clamped hypoglycemia (approx. 2.5 mmol/L 1x2h) and once following.